Reply by Farkled

The larger the plane, the less you should wish to flatten it yourself. Can you guarantee that the substrate you use to flatten against is flat? Within .0005” ? If you can’t do that then flattening doesn’t matter. More to the point: use the plane. If it planes well, then no flattening is required. Move on with life. If it does not plane well, either have it professionally ground or go buy another plane.